Fatty acid synthase (FASN) is a key enzyme for the synthesis of long-chain fatty acids from acetyl-coenzyme A (CoA) and malonyl-CoA that uses reduced nicotinamide adenine dinucleotidephosphate as a cofactor. The final step in the de novo synthesis of fatty acids in mammalians is carried out by FASN, a 250 kDa protein containing 7 functional domains. Through an iterative enzymatic reaction, FASN produces palmitate starting from the substrates acetylCoA and malonylCo, using NADPH (as defined below) as a cofactor (See, MAIER, T., et al., “Architecture of mammalian fatty acid synthase at 4.5 Å resolution”, Science, 2006, pp 1258-1262, Vol. 311).
FASN is minimally expressed in most normal human tissues except the liver and adipose tissue, where it is expressed at high levels. Except for these lipogenic tissues (such as liver, lactating breast, fetal lung, and adipose tissue), FASN has a low expression in normal cells which use fatty acids from the diet, while tumor cells largely depend on de novo fatty acid synthesis. FASN expression is highly up-regulated in various tumors, e.g. prostate, breast, colon, and lung cancer (See, SWINNEN, J. V., et al., “Stimulation of tumor-associated fatty acid synthase expression by growth factor activation of the sterol regulatory element-binding protein pathway”. Oncogene, 2000, pp 5173-5181, Vol 19; KUHAJA, F. P., “Fatty-acid synthase and human cancer: new perspectives on its role in tumor biology”, Nutrition, 2000, pp 202-208, Vol. 16).
FASN overexpression leads to growth and survival advantage to the tumors achieved through multiple mechanisms. Firstly, it provides lipids for membrane synthesis. Moreover, the more saturated lipid composition of the membranes increases resistance to chemotherapy. FASN also contributes to improved growth factor receptor expression in lipid rafts (See, SWINNEN, J. V., et al., “Fatty acid synthase drives the synthesis of phospholipids partitioning into detergent resistant membrane microdomains”, Biochem. Biophys. Res. Commun., 2000, pp 898-903, Vol. 302; MENENDEZ, J. A., et al., “Inhibition of fatty acid synthase (FAS) suppresses HER2/neu (erbB-2) oncogene overexpression in cancer cells”, Proc. Natl Acad. Sci. USA, 2004, pp 10715-10720, Vol. 101), and improved cell signalling. Lastly, the NAPDPH consumption during palmitate synthesis in tumor cells keeps the redox balance in check.
In tumor cells, but not in normal cells, siRNA knock down or pharmacological inhibition of FASN results in apoptosis in vitro, and in a delayed tumor growth in vivo. The role of FASN as a potential oncogene has been further established in mouse models. Transgenic mouse models with FASN over expression in the prostate develop invasive prostate cancer in the presence of Androgen Receptor (See, MIGITA, et al., “Fatty Acid Synthase: A Metabolic Enzyme and Candidate Oncogene in Prostate Cancer”, J Natl. Cancer Inst., 2009, pp 519-532, Vol. 101). It has been proposed that FASN exerts its oncogenic effect by inhibiting the intrinsic pathway of apoptosis. Androgens and epidermal growth factor (EGF) up-regulate FASN expression and activity. In addition, FASN is also over expressed in androgen-independent prostate cancers most likely through activation of the PI3K/Akt pathway (See, BANDYOPADHYAY, S., et al., “FAS expression inversely correlates with PTEN level in prostate cancer and a PI-3 kinase inhibitor synergizes with FAS siRNA to induce apoptosis”, Oncogene, 2005, pp 5389-5395, Vol. 24; VAN DE DANDE, T., et al., “Role of the phosphatidylinositol 3′-kinase/PTEN/Akt kinase pathway in the overexpression of fatty acid synthase in LNCaP prostate cancer cells”, Cancer Res., 2002, pp 642-646, Vol. 62; PORTSMANN, T., et al., “PKB/AKT induces transcription of enzymes involved in cholesterol and fatty acid biosynthesis via activation of SREBP”, Oncogene, 2005, pp 6465-6481, Vol. 24). Thus, FASN is emerging as an important target for cancer therapy.
Since FASN expression is markedly increased in several human cancers compared with the corresponding normal tissue, and FASN overexpression in tumors has been associated with a poor prognosis, FASN inhibitors are viewed as potential therapeutics for the treatment of cancer. There remains a need for pharmaceutical agents for the treatment of a variety of cancers, including breast, prostate, head, neck, skin, lung, ovary, endometrium, thyroid, colon, rectum, esophagus, stomach, kidney, liver, bladder, pancreas, brain, blood, bone, and others.
FASN inhibitors have also shown promise in the treatment of other FASN-mediated diseases, disorders or conditions, such as, obesity, lack of appetite control, and inflammatory conditions. Additionally, FASN has been implicated in diabetes and/or regulation of the general wellness of the liver, and therefore has potential in the treatment of obesity, Type II diabetes mellitus, Syndrome X, and disorders of the liver; the treatment of which there remains a need for pharmaceutical agents.